Display device comprising pixel portion

ABSTRACT

To provide a liquid crystal display device having high quality display by obtaining a high aperture ratio while securing a sufficient storage capacitor (Cs), and at the same time, by dispersing a load (a pixel writing-in electric current) of a capacitor wiring in a timely manner to effectively reduce the load. A scanning line is formed on a different layer from a gate electrode and the capacitor wiring is arranged so as to be parallel with a signal line. Each pixel is connected to the individually independent capacitor wiring via a dielectric. Therefore, variations in the electric potential of the capacitor wiring caused by a writing-in electric current of a neighboring pixel can be avoided, whereby obtaining satisfactory display images.

This application is a division of application Ser. No. 10/456,503, filedon Jun. 9, 2003, now U.S. Pat. No. 7,098,086, which is a division ofapplication Ser. No. 09/653,535, filed on Aug. 31, 2000, now U.S. Pat.No. 6,583,472.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having a circuitconstructed of a thin film transistor (hereinafter referred to as TFTs)and a method of manufacturing the same. For example, the presentinvention relates to an electro-optical device typified by a liquidcrystal display panel, and electronic equipment having such anelectro-optical device mounted thereon as a part.

It is to be noted that a semiconductor device as used herein throughoutthe present specification denotes a general device which functions byutilizing semiconductor characteristics, and that electro-opticaldevices, semiconductor circuits, and electronic equipments are allsemiconductor devices.

2. Description of the Related Art

Techniques for structuring a thin film transistor (TFT) using asemiconductor thin film (having a thickness on the order of aboutseveral to several hundred nm) formed on a substrate having aninsulating surface have been in the spotlight in recent years. Thin filmtransistors are widely applied to electronic devices such as an IC or anelectro-optical device, and in particular, development of the TFT as aswitching element of a liquid crystal display device is proceedingrapidly.

In order to obtain high quality images in the liquid crystal displaydevice, an active matrix type liquid crystal display device thatutilizes TFTs as switching elements to be connected to respective pixelelectrodes which are arranged in matrix is attracting much attention.

It is necessary that the electric potential of an image signal is heldin each pixel electrode connected to the TFTs until the next write-intime in order to perform good quality display in the active matrix typeliquid crystal display device. Generally, the provision of a storagecapacitor (Cs) in each pixel holds the electric potential of the imagesignal.

Various proposals have been made for the structure and the formationmethods of the above stated storage capacitor (Cs). However, from theviewpoint of reliability or simplicity of the manufacturing process, itis preferable that, of the insulating films for structuring a pixel, agate insulating film of a TFT, which has the highest quality is utilizedas a dielectric of the storage capacitor (Cs). Conventionally, as shownin FIG. 18, a capacitor wiring that becomes an upper electrode is firstprovided by utilizing a scanning line, and then the formation of thestorage capacitor (Cs) is carried out by using the upper electrode(capacitor wiring), a dielectric layer (gate insulating film), and alower electrode (semiconductor film).

Also, from the viewpoint of display performances, there is a demand forgiving pixels larger storage capacitors as well as making the apertureratio higher. Efficient utilization of a back light is improved if eachpixel has a high aperture ratio. Consequently, the amount of back lightfor obtaining a predetermined display luminance can be restrained, andtherefore attainment of a power-saving and small scale display devicecan be achieved. Furthermore, each pixel is provided with a largestorage capacitor, thereby improving the characteristic of each pixel inholding display data, to improve the display quality. In addition, incase of point sequential driving of the display device, a signal storagecapacitor (sample hold capacitor) is required in the driver circuit sideof each signal line. However, with the provision of a large storagecapacitor in each pixel, a surface area occupied by the sample holdcapacitor can be made smaller, and therefore the display device can bemade smaller.

Such demands become problems in proceeding with the progress of makingthe pitch of each display pixel microscopic which accompanies theprogress of making a liquid crystal display device smaller and highdefinition (increasing the number of pixels).

There is an additional problem in that it is difficult to make a highaperture ratio and a large storage capacitor compatible with each otherin the above stated conventional pixel structure.

An example in which a conventional pixel structure having the size of apixel formed to 19.2 μm in accordance with the design rule of Table 1 isshown in FIG. 18.

TABLE 1 Si layer: minimum size = 0.8 μm, minimum spacing = 1.5 μm Gateelectrode: minimum size = 1.0 μm, minimum spacing = 1.5 μm Scanningline: minimum size = 1.5 μm, minimum spacing = 1.5 μm Contact hole ofsignal line and Si layer: minimum size = 1.0 μm□ margin of the contacthole and the Si layer = 1.0 μm minimum spacing of the contact hole andthe scanning (gate electrode) line = 1.3 μm Signal line: minimum size =1.5 μm, minimum spacing = 1.5 μm margin of the contact hole and thesignal line = 1.3 μm Pixel size: 19.2 μm□ Pixel TFT: L = 1.5 μm, W = 0.8μm, single gate Scanning line: minimum size of the wiring width = 1.0 μmScanning line: minimum size of the wiring width at a portion ofoverleaping Si layer = 1.5 μm Capacitor wiring: minimum size = 2.0 μm

A characteristic of the conventional pixel structure is that two wirings(a scanning line and a capacitor wiring) are arranged parallel to eachother in relation to the continuous formation of the two respectivewirings, the scanning line and the capacitor wiring. In FIG. 18,reference numeral 10 denotes a semiconductor film, 11 denotes a scanningline, 12 denotes a signal line, 13 denotes an electrode, and 14 denotesa capacitor wiring. Note that FIG. 18 is a simplified top view of thepixel, and therefore a pixel electrode that is connected to theelectrode 13 and a contact hole that reaches the electrode 13 are bothnot shown in the figure.

Thus, in the case of structuring the storage capacitor with a upperelectrode (capacitor wiring), a dielectric layer (gate insulating film),and a lower electrode (semiconductor film), all the circuit elements (apixel TFT, a storage capacitor, a contact hole, ect.) necessary forstructuring a circuit of the pixel become elements relevant to a gateinsulating film. Accordingly, these elements constituting the circuitelements are arranged almost planarly within each pixel.

Therefore, it is crucial to efficiently layout the circuit elements thatare necessary for constructing the circuit of the pixel in order toattain both a high aperture ratio and a large storage capacitor of eachpixel within the regulated pixel size. In other words, from the factthat all the circuit elements are in connection with the gate insulatingfilm, it can be said that it is essential to improve the efficiency ofutilizing the gate insulating film.

Thus, from the above perspective, an efficient planar layout of theexample of the circuit structure of a pixel of FIG. 18 is shown in FIG.19. In FIG. 19, reference numeral 21 denotes a single pixel region, 22denotes a pixel opening region, 23 denotes a storage capacitor region,24 denotes an A region, and 25 denotes a portion of the TFT and acontact region.

With respect to the area of the pixel opening region 22 which is 216.7μm² (aperture ratio of 5.8.8%) as shown in FIG. 19, it is composed ofthe areas of the storage capacitor region 23 which is 64.2 μm², theportion of the TFT and the contact region 25 which is 42.2 μm², and theA region 24 which is 34.1 μm².

The A region 24 is a segregation region of the scanning line and thecapacitor wiring which originated from the fact that a wiring portionfor mutually connecting a region that functions as a gate electrode of aTFT, the scanning line and the capacitor wiring are arranged parallel toeach other. The gate insulating film of the A region is not rendered itsoriginal function, becoming a cause of reducing the efficiency oflayout.

Further, in the case of the above structure, there is a problem in thatthe demand for a capacitor wiring resistance has become strict.

In a normal liquid crystal display device drive, the writing-in of theelectric potential of the image signal to the plurality of pixelsconnected to each scanning line is performed consecutively in thescanning line direction (in the case of the point sequential drive) orall at the same time (in the case of the linear sequential drive).

In terms of arranging the capacitor wiring and the scanning lineparallel to each other in the pixel structure as stated above, theplurality of pixels connected to the respective scanning lines areconnected to a common capacitor wiring. Therefore, opposing electriccurrents for a plurality of pixels corresponding to the pixel writing-inelectric current continuously or simultaneously flow in the commoncapacitor wiring. In order to avoid a reduction in display qualitycaused by the electric potential variation of the capacitor wiring, itis necessary to sufficiently lower the capacitor wiring resistance.

However, widening the width of the wiring for lowering the resistance ofthe capacitor wiring means that the surface area of the storagecapacitor is enlarged while the aperture ratio of the pixel is reduced.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems as asolution for the designing side, and therefore has an object to providea liquid crystal display device having high quality display by obtaininga high aperture ratio while securing a sufficient storage capacitor(Cs), and at the same time, by dispersing a load (a pixel writing-inelectric current) of the capacitor wiring in a timely manner toeffectively reduce the load.

The structure of the invention disclosed in the present specification isa semiconductor device, characterized by comprising:

a first wiring on an insulating surface;

a first insulating film on said first wiring;

a semiconductor film on said first insulating film;

a second insulating film on said semiconductor film;

a second wiring and a gate electrode to be connected to said firstwiring on said second insulating film;

a third insulating film on said second wiring and said gate electrode;and

a third wiring to be connected to said semiconductor film on said thirdinsulating film.

In the above-mentioned structure, the semiconductor device ischaracterized in that the semiconductor film and the second wiringoverlap via the second insulating film.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that a storage capacitor is formed with thesecond insulating film as a dielectric in a region where the secondwiring and the semiconductor film overlap via the second insulatingfilm.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that an impurity element that imparts aconductivity type is doped into the region of the semiconductor filmwhere the second wiring overlaps via the second insulating film.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized by further comprising an electrode to beconnected to the semiconductor film and a pixel to be connected to theelectrode on the third insulating film.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the first wiring and the second wiringare arranged in a direction orthogonal with each other.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the first wiring is arranged in adirection orthogonal to the third wiring.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the gate electrode is formed on adifferent layer from the first wiring.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the gate electrode is patterned into anisland shape.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the first wiring comprises a scanningline.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the second wiring comprises a capacitorwiring.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the third wiring comprises a signalline.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the second insulating film comprises agate insulating film.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the gate electrode is made of a filmhaving as its principal constituent an element selected from the groupconsisting of poly-Si, W, WSi_(x), Al, Ta, Cr, or Mo which have beendoped with an impurity element that imparts a type of conductivity, or alamination film of a combination of these elements.

Further, the structure of another invention is a semiconductor device,characterized by comprising:

a plurality of signal lines arranged parallel to each other at apredetermined interval and connected to a signal line driver circuit;

a plurality of scanning lines arranged parallel to each other at apredetermined interval and connected to a scanning line driver circuit;and

a capacitor wiring arranged parallel to the signal line.

Further, in the above-mentioned structures, the semiconductor device ischaracterized in that the scanning lines are orthogonal to the signallines.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized by further comprising a thin film transistorhaving a gate electrode connected to the scanning line which isorthogonal to the signal line and a pixel electrode connected to thethin film transistor.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the gate electrode is formed on adifferent layer from the scanning line.

Further, in the above-mentioned respective structures, the semiconductordevice is characterized in that the gate electrode is patterned into anisland shape.

Further, the structure of the invention to attain the above structure isa method of manufacturing a semiconductor device, characterized bycomprising:

a first step of forming a first wiring on a substrate having aninsulating surface;

a second step of forming a first insulating film on the first wiring;

a third step of forming a semiconductor film on the first wiring;

a fourth step of forming a second insulating film on the semiconductorfilm;

a fifth step of forming a first contact hole reaching the first wiringby selectively etching the first insulating film and the secondinsulating film;

a sixth step of forming a gate electrode on the second insulating filmoverlapping a portion of the semiconductor film and connected to thefirst wiring through the first contact hole;

a seventh step of forming a third insulating film on the gate electrode;

an eighth step of forming a second contact hole reaching thesemiconductor film by selectively etching the second insulating film andthe third insulating film; and

a ninth step of forming a third wiring on the third insulating filmconnected to the semiconductor film through the second contact hole.

Further, in the above-mentioned structure, the manufacturing method ischaracterized in that a second wiring is formed on the second insulatingfilm to overlap a portion of the semiconductor film in the same step asforming the gate electrode.

Further, in the above-mentioned structure, the manufacturing method ischaracterized by further comprising a step of partially thinning thesecond insulating film that overlaps the second wiring after the step offorming the second insulating film on the semiconductor film.

Further, in the above-mentioned structure, the manufacturing method ischaracterized in that the second insulating film is a gate insulatingfilm, the first wiring is a scanning line, the second wiring is acapacitor wiring, and the third wiring is a signal line.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a top view of a pixel;

FIG. 2 is a diagram showing a circuit structure of a TFT substrate;

FIGS. 3A and 3B are diagrams showing cross-sectional views of the TFTsubstrate;

FIG. 4 is a diagram illustrating the cross-sectional structure of anactive matrix type liquid crystal display device;

FIG. 5 is a view showing the outer appearance of an AM-LCD;

FIGS. 6A to 6F are diagrams showing examples of electronic equipment;

FIGS. 7A to 7D are diagrams showing examples of electronic equipment;

FIGS. 8A to 8C(1) and FIG. 8C(2) are cross-sectional views and a topview, respectively, showing a process of manufacturing a pixel portion;

FIGS. 9A to 9C(1) and FIG. 9C(2) are cross-sectional views and a topview, respectively, showing a process of manufacturing a pixel portion;

FIGS. 10A to 10C(1) and FIG. 10C(2) are cross-sectional views and a topview, respectively, showing a process of manufacturing a pixel portion;

FIGS. 11A and 11B(1) and FIG. 11B(2) are cross-sectional views and a topview, respectively, showing a process of manufacturing a pixel portion;

FIGS. 12A (1) and 12B (2) are a cross-sectional view and a top view,respectively, showing a process of manufacturing a pixel portion;

FIG. 13 is a graph illustrating a TFT characteristic;

FIG. 14 is a diagram showing a top view of a pixel;

FIGS. 15A and 15B are diagrams showing cross-sectional views of a pixelstructure;

FIG. 16 is a diagram showing cross-sectional view of a pixel structure;

FIGS. 17A and 17B are is a diagram showing a top view of a pixel;

FIG. 18 is a top view of a conventional pixel; and

FIG. 19 is a view showing a conventional pixel opening region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed.

The present invention is characterized in that a scanning line is formedon a different layer from a gate electrode in order to increase anaperture ratio as well as to increase a storage capacitor. An example ofa pixel structure of the present invention is shown in FIG. 1.

In FIG. 1, a gate electrode 106 formed into an island shape bypatterning is connected to a scanning line 102 through a contact hole100 c formed at an insulating film. Further, a semiconductor film 104 isconnected to a signal line 109 through a contact hole 100 a. Inaddition, the semiconductor film 104 is connected to an electrode 110through a contact hole 100 b. A region of the semiconductor film that isconnected to the signal line 109 or the electrode 110 is referred to asa source region or a drain region. Further, a channel forming region isformed between the source region and the drain region, and the gateelectrode 106 is present on the channel forming region through a gateinsulating film. Note that the source region, the drain region, and thechannel forming region are not shown in the figure for simplification.

According to the present invention, in the case of forming the scanninglines 102 on the lower layer of the gate electrode 106 as shown in FIG.1, the scanning lines 102 will be provided on the lower layer of thesemiconductor film 104, thus making it possible to function as a lightshielding film. In addition, the storage capacitor is formed with thelower electrode as the semiconductor film, the insulating film coveringthe semiconductor film as a dielectric, and the upper electrode as acapacitor wiring 107. It is to be noted that the storage capacitor maybe enlarged by partially thinning the insulating film which covers thesemiconductor film.

Further, according to an aspect of the present invention, TFTs of eachpixel can be a dual gate structure in which a gate electrode is providedon the upper and lower part of the channel forming region through aninsulating film, and the storage capacitor formed of the scanning lineand another wiring can be restrained while improving the characteristicsof the TFTs by setting the film thickness of a first insulating filmappropriately.

The present invention, unlike the prior art (the capacitor wiring isarranged parallel with the scanning line), is characterized in that thecapacitor wiring is arranged so that it is parallel with the signalline. Accordingly, good display image can be obtained since variationsin the electric potential of the capacitor wiring due to a writing-incurrent of a neighboring pixel are avoided because each pixel isconnected to storage capacitors formed of respective independentcapacitor wirings even if consecutive writing-in of the image signals isperformed to the pixels corresponding to each scanning line under thedriving method.

Conventionally, a sample hold capacitor is provided in each signal linein order to prevent the signal line electric potential (a writingelectric potential) from being reduced during a writing period to eachscanning line. In the present invention, the capacitor wiring isarranged parallel with and overlapping the signal line. Therefore, it isnot necessary to provide the sample hold capacitor in a portion of theperipheral circuit from the fact that the parasitic capacitance of thesignal line increases, thereby improving the holding characteristics ofthe signal line electric potential. In comparison with the prior art,the peripheral circuits can be made smaller.

In addition, the demand performance for the capacitor wiring resistancehas been alleviated because of the same reasons as the above, andtherefore there is more degree of freedom in designing the arrangement,size, and film thickness of the capacitance wiring. Furthermore, becausethe selection range of the materials for the capacitor wiring haswidened, the degree of complication in designing and manufacturing haslessened, leading to the attainment of a higher production yield.

Regarding the present invention composed of the above aspect, a detaileddescription will be made of the embodiments shown in the following.

Embodiment 1

Hereinafter, embodiments of the present invention will be describedtaking a point sequential drive of a projector type liquid crystaldisplay device as an example.

An active matrix type liquid crystal display device utilizing a TFT asits switching element is constructed of a substrate (TFT substrate) withpixel electrodes arranged in matrix and an opposing substrate withopposing electrodes formed thereon arranged facing the TFT substrate viaa liquid crystal layer. The space between the two substrates arecontrolled at a predetermined interval via spacers, etc. and a sealingmaterial is used around the outer periphery portion of the displayregion to enclose the liquid crystal layer.

FIG. 4 is a view schematically showing a cross-sectional structure ofthe liquid crystal display device of the present embodiment. In FIG. 4,reference numeral 101 denotes a substrate (TFT substrate), 102 denotesthe scanning lines, 103 denotes a first insulating film, 104 denotes thesemiconductor film, 105 denotes a gate insulating film (a secondinsulating film), 106 denotes the gate electrode, 107 denotes acapacitor wiring, 108 denotes a third insulating film, and 109 and 111denote signal lines or electrodes diverged from the signal lines.Reference numeral 110 denotes an electrode which is connected to thesemiconductor film through a contact hole (not shown in the figure)which is formed with the third insulating film. Further, the gateelectrode 110 is an electrode for connecting the TFTs to the pixelelectrodes.

It is to be noted that throughout the present specification, the term“electrode” implies a part of the “wiring” and indicates a place atwhich the wiring is electrically connected with another wiring, or aplace at which the wiring intersects a semiconductor layer. Thus, forthe sake of explanation conveniences, the terms “wiring” and “electrode”are used distinguishably. However, the term “electrode” shall alwaysinclude the meaning of “wiring”.

Note that portions denoted by the reference numerals 101 to 110 aredefined as TFTs throughout the present specification. In addition,reference numerals 109 and 110 may be an electrode diverged from awiring or a wiring.

Furthermore, reference numeral 112 denotes a fourth insulating filmwhich covers the TFTs, 113 denotes a light shielding film for preventingthe TFTs from light deterioration, 114 denotes a fifth insulating film,115 denotes a pixel electrode connected to the electrode 110 through acontact hole 100 d, and 116 denotes an alignment film for orientating aliquid crystal layer 117.

Also in FIG. 4, an opposing electrode 119 and an alignment film 118 areprovided on an opposing substrate 120, and besides, a light shieldingfilm and a color filter may be provided when necessary.

The substrate (TFT substrate) 101 comprises a pixel portion 201, and ascanning line driver circuit 202 and a signal line driver circuit 203formed in the periphery thereof as shown in FIG. 2.

The scanning line driver circuit 202 is mainly composed of shiftregisters for sequentially transmitting scanning signals. The signalline driver circuit 203 is mainly composed of sample hold circuits forholding an image signal and driving a signal line after sampling a shiftregister and the image signal that is inputted on the basis of an outputof the shift register.

In the pixel portion 201, a plurality of scanning lines (gate wirings)207 connected to the scanning line driver circuit 202 and arrangedparallel to each other at a predetermined interval and a plurality ofsignal lines 208 connected to the signal line driver circuit 203 with aterminal for inputting an image signal 205 and arranged parallel to eachother at a predetermined interval. The scanning lines 207 are orthogonalto the signal lines 208. Together with arranging TFTs (not shown in thefigure) at each point of intersection, pixel electrodes (not shown inthe figure) are arranged in the respective regions marked off by thescanning lines and signal lines. Thus, each pixel electrode is arrangedin matrix from this structure. In addition, a plurality of capacitorwirings 209 connected to a GND (ground) or a fixed electric potential206 are provided parallel to the signal lines 208. Reference numeral 204denotes a driver circuit disposed on an opposing substrate. It is to benoted that for simplification, only a few lines of the signal lines, thescanning lines, and the capacitor wirings are shown in FIG. 2.

Hereinafter, a simplified process of manufacturing a semiconductordevice shown in FIG. 4 is described with references to FIGS. 1, 3A, and3B.

First, besides a glass substrate as the substrate 101, a quartzsubstrate and a plastic substrate can also be used. In the case of usinga glass substrate, heat treatment may be performed in advance at atemperature that is approximately 10 to 20° C. lower than the distortionpoint of glass. Furthermore, a base film is formed on the surface of thesubstrate 101 on which the TFTs will be formed in order to prevent thediffusion of impurities from the substrate 101. The base film is made ofan insulating film such as a silicon oxide film, a silicon nitride film,or a silicon oxynitride film.

Next, a conductive film is formed on the substrate and then patterningis performed to thereby form the scanning lines 102. Conductivematerials such as poly-Si, WSi_(x) (X=2.0 to 2.8), Al, Ta, W, and Crwhich have been doped with an impurity element that imparts a type ofconductivity and a laminated structure thereof can be used for thescanning lines 102. In this embodiment, the scanning lines 102, arrangedat a predetermined interval, are formed of a laminated structurecomposed of a WSi_(x) film (film thickness: 100 nm) and a poly-Si film(film thickness: 50 nm), which are conductive materials having highlight blocking characteristics.

Covering the scanning lines 102 and having a film thickness of about 500nm, the first insulating film 103 is formed next. An insulating filmcontaining silicon formed by known methods such as plasma CVD orsputtering is used for the first insulating film 103. In addition, thefirst insulating film 103 may be formed of a film made of an organicinsulating material, a silicon oxide film, a silicon oxynitride film, ora silicon nitride film, or a lamination film of a combination of thesefilms.

The semiconductor film is formed next to a thickness of between 25 and80 nm (preferably between 30 and 60 nm) by known methods such as plasmaCVD or sputtering, and then patterned into a desired shape. In thisembodiment, an amorphous silicon film is formed to about 50 nm thick byplasma CVD. With a known crystallization method, a crystallizationprocess is performed to form a crystalline silicon film (poly-Si) fromthe amorphous silicon film. Then patterning is conducted on thecrystalline silicon film to pattern it into an island shape. Althoughthe present embodiment uses a crystalline silicon film (poly-Si), noparticular limitations are placed as long as it is a semiconductor film.Note that throughout the present specification, the term “semiconductorfilm” denotes a single crystal semiconductor film, a crystallinesemiconductor film (such as poly-Si), an amorphous semiconductor film(such as a-Si), or a microcrystalline semiconductor film. Further, acompound semiconductor film such as a silicon germanium film is alsoincluded as the “semiconductor film”.

An insulating film containing silicon formed by methods such as plasmaCVD or sputtering, or an oxide film formed of a semiconductor film (suchas an Si film) which has been thermally oxidized is used to form thesecond insulating film (gate insulating film) 105. The second insulatingfilm 105 may be a laminate structure made up of a plurality of layerssuch as two layers or three layers when necessary.

Thereafter, in order to construct a TFT that functions as an imagesignal writing-in switch, with utilization of the respective islandshape semiconductor films, a known technique is employed to selectivelydope an impurity element (such as phosphorus or boron) that imparts ap-type or an n-type conductivity into the island shape semiconductorfilm, thereby forming a low resistance source region and drain region,and further forming a low resistance region. This low resistance regionis similar to the drain region in that it is doped with an impurityelement (typically phosphorus or boron) and is a part of thesemiconductor films that have been made low resistance. Note that theorder of the process of selectively doping the impurity element is notparticularly limited. For example, the impurity element may be dopedbefore the formation of the first insulating film and the gateelectrode, or after the formation of the gate electrode. In addition, anLDD region and an offset region may be formed in response to the circuitstructure. It is to be noted that the respective regions are not shownin the figure for simplification.

Thus, a channel forming region is formed between the source region andthe drain region in the semiconductor film 104.

Next, selective etching is performed on the the first insulating film103 and the second insulating film 105 to thereby form the first contacthole 100 c shown in FIG. 3B reaching the scanning lines 102.

A conductive film is formed next on the second insulating film 105. Thenpatterning is performed to form the gate electrode 106 and the capacitorwiring 107. The gate electrode 106 and the capacitor wiring 107 areformed at the thickness of about 300 nm with conductive materials suchas poly-Si, WSi_(x) (X=2.0 to 2.8), Al, Ta, W, Cr, and Mo which 0.25have been doped with an impurity element that imparts a type ofconductivity, and a laminated structure thereof. Further, a single layermay be formed for the gate electrode 106 and the capacitor wiring 107,but a laminate structure made up of a plurality of layers such as twolayers or three layers may also be formed when necessary. In this case,each gate electrode formed into an island shape is electricallyconnected to the scanning lines 102 via the first contact hole 100 cwhich is formed with the first insulating film 103 and the secondinsulating film 105.

The island shape gate electrode 106 is arranged on the channel formingregion of each pixel through the second insulating film 105. Further,the capacitor wirings 107 are arranged on the low resistance regionthrough the second insulating film 105. Note that the storage capacitormay be enlarged by adding a process in which the film of a region wherethe capacitor wirings 107 overlap the second insulating film 105 ispartially thinned. The capacitor wirings 107 are also arrangedcontinuously to each pixel in the signal line direction and electricallyconnected outside the display region to the ground or to the fixedelectric potential.

The third insulating film 108 is formed next covering the gate electrode106 and the capacitor wirings 107. An insulating film containing siliconformed by methods such as plasma CVD or sputtering is used for the thirdinsulating film 108. In addition, the third insulating film 108 may beformed of a silicon oxide film, a silicon oxynitride film, a siliconnitride film, or a lamination film of a combination of these films.

Next, selective etching is performed on the the second insulating film105 and the third insulating film 108 to thereby form the second contactholes 100 a and 100 b shown in FIGS. 3A and 3B, respectively, to reachthe semiconductor film (the source region or the drain region).

A film having Al, W, Ti, and TiN as its main component or a conductivefilm (film thickness: 500 μm) having a laminated structure of theseelements is next formed on the third insulating film 108. Thenpatterning is performed, thereby forming the signal lines 109 and 111and the island shape electrode 110 for connection with a pixel electrodewhich will be formed later. The signal lines 109 and 111 are connectedto either the source region or the drain region through the secondcontact holes 100 a and 100 b that reach the semiconductor film.Similarly, the island shape electrode 110 is connected to either thesource region or the drain region through the second contact hole 100 athat reaches the semiconductor film. Furthermore, the signal lines 109and 111 are arranged in a direction parallel to the capacitor wirings107.

The island shape electrode 110 is arranged so as to be isolated from thesignal line 109. However, both the signal line 109 and the island shapeelectrode 110 will not be connected to the source region together.Similarly, both the signal line 109 and the island shape electrode 110will not be connected to the drain region together.

A top view of the pixel at this stage corresponds to FIG. 1, and theschematic views of the cross-sectional structure in which the crosssections are taken along the broken line A-A′ and the broken line B-B′in FIG. 1 correspond to FIGS. 3A and 3B respectively.

The fourth insulating film 112 is formed next covering the signal line109 and the island shape electrode 110. The fourth insulating film 112may be formed of a film such as an organic insulating material film, asilicon oxide film, a silicon oxynitride film or a silicon nitride film,or a lamination film of a combination of these films.

Subsequently, a film having high light shielding characteristics formedof materials such as Ti, Al, W, Cr, or black-colored resin is formed onthe fourth insulating film 112 and then patterned into a desired shape,thereby forming the light shielding film 113. The light shielding film113 is arranged mesh like so that other areas, except the openingportion of the pixel, are shielded from light.

In Embodiment 1, although the light shielding film 113 becomeselectrically floating, if a low resistance film is selected as thematerial for the light shielding film, then it is possible to controlthe light shielding film to an optional electric potential outside thedisplay portion.

A fifth insulating film 114 is formed next on the light shielding film113. It is appropriate to form the fifth insulating film 114 with a filmmade of an organic insulating material. By forming the fifth insulatingfilm 114 with an organic insulating material, the surface can besufficiently flattened. In addition, parasitic capacitance can bereduced since organic resin materials are generally low in dielectricconstant. However, because organic resin materials are absorbent, theyare not suitable as protection films. Thus, the fifth insulating film114 may be a laminate structure with combinations of a silicon oxidefilm, a silicon oxynitride film, and a silicon nitride film.

Next, selective etching is performed on the the fourth insulating film112 and the fifth insulating film 114 to thereby form the third contacthole 100 d to reach island shape electrode. The third contact hole 100 dis indicated by the broken line in FIG. 4 for the sake of convenience.

A transparent conductive film such as an ITO film is formed next andthen patterned to thereby form the pixel electrode 115. The pixelelectrode 115 is connected to the island shape electrode 110 through thethird contact hole 100 d. The respective pixel electrodes are eachindependently arranged so as to cover the opening portion of each pixel.

The alignment film 116 for orientating the liquid crystal layer 117 isformed on the TFT substrate thus formed. Then the TFT substrate and theopposing substrate 120, which is provided with the opposing electrode119 and the alignment film 118, are joined together by using a knowncell construction technique. Thereafter, a liquid crystal material isinjected between both substrates and enclosed therein. The liquidcrystal cell in which the liquid crystal layer is held between the twosubstrates, is thus completed.

By employing the above described manufacturing steps, and furthermorearranging the wirings, the semiconductor film, etc. in accordance withthe design rules of Table 2, a surface area of 236.9 μm² of the pixelopening region (aperture ratio: 64.3%) and a surface area of 62.8 μm² ofthe storage capacitor region can be obtained.

TABLE 2 Si layer: minimum size = 0.8 μm, minimum spacing = 1.5 μm Gateelectrode: minimum size = 1.0 μm, minimum spacing = 1.5 μm A contacthole of the scanning line and the gate electrode: minimum size = 1.0 μmmargin of the contact hole and the gate electrode = 1.0 μm Scanningline: minimum size = 1.5 μm, minimum spacing = 1.5 μm Contact hole ofsignal line and Si layer: minimum size = 1.0 μm□ margin of the contacthole and the Si layer = 1.0 μm minimum spacing of the contact hole andthe scanning (gate electrode) line = 1.3 μm Signal line: minimum size =1.5 μm, minimum spacing = 1.5 μm margin of the contact hole and thesignal line = 1.3 μm Pixel size: 19.2 μm□ Pixel TFT: L = 1.5 μm, W = 0.8μm, single gate Scanning line: minimum size of the wiring width = 1.0 μmScanning line: minimum size of the wiring width at a portion ofoverleaping Si layer = 1.5 μm Capacitor wiring: minimum size = 2.0 μm

In Embodiment 1, the provision of a region for the contact hole 100 cfor connecting the gate electrode 106 and the scanning line 102 isrequired in the restructured pixel region. Further, in Embodiment 1, anupper light shielding film is only the film for shielding the peripheralportion of the channel forming region of the island shape Si film fromlight. Accordingly, it is desired that the structure be provided with anupper light shielding film.

According to the present structure, because the scanning lines 102function as a lower light shielding film to the channel forming regionand the peripheral portion thereof, light incident from the liquidcrystal layer 117 is reflected at the lower interface of the TFTsubstrate and then become incident on the channel forming region and theperipheral portion thereof. Accordingly, the occurrence of light leakingfrom the TFT can be prevented, making it possible to obtain betterdisplay quality.

Embodiment 2

A structure of the active matrix type liquid crystal display deviceshown in Embodiment 1 will be described here in Embodiment 2 withreference to the perspective view of FIG. 5. It is to be noted that thesame reference numerals designate components corresponding to those inEmbodiment 1.

In FIG. 5, a matrix substrate is composed of a pixel portion, a scanningline driver circuit 802, a signal line driver circuit 803, and othersignal processing circuits formed on a substrate 101. A pixel TFT 800and a storage capacitor 200 are provided in the pixel portion, and thedriver circuits provided in the periphery thereof are structured basedon a CMOS circuit.

Further, the capacitor wiring 107 is provided in a direction parallelwith the signal line 109 and functions as the upper electrode of thestorage capacitor 200. The capacitor wiring 107 is also connected to theground or to a fixed electric potential.

The scanning line 102 and the signal line 109, from the scanning linedriver circuit 802 and the signal line driver circuit 803, respectively,extend to the pixel portion and are connected to the pixel TFT 800.Further, an FPC (Flexible Printed Circuit) 804 is connected to anexternal input terminal 805 to be utilized for inputting signals such asimage signals. The FPC 804 is firmly fixed with a reinforced resin. Thenconnecting wirings 806 and 807 are connected to the respective drivercircuits. Though not shown in the figure, a light shielding film and atransparent electrode are provided on an opposing substrate 808.

Embodiment 3

The pixel matrix circuit formed by implementing the present inventioncan be used in various electro-optical devices (active matrix typeliquid crystal display device, active matrix EL display, and activematrix EC display). That is, the present invention can be implemented inall electronic equipment that incorporate these electro-optical devicesas a display portion.

The following can be given as such electronic equipment: a video camera,a digital camera, a projector (a rear type or a front type), a headmount display (goggle type display), a car navigation system, a personalcomputer, a portable information terminal (such as a mobile computer, acellular phone, and an electronic book) etc. Some examples of these areshown in FIGS. 6A to 6F and FIGS. 7A to 7D.

FIG. 6A shows a personal computer that is comprised of a main body 2001,an image input portion 2002, a display portion 2003, and a keyboard2004. The present invention can be applied to the display portion 2003.

FIG. 6B shows a video camera that is comprised of a main body 2101, adisplay portion 2102, an audio input portion 2103, operation switches2104, a battery 2105, and an image receiving portion 2106. The presentinvention can be applied to the display portion 2102.

FIG. 6C shows a mobile computer that is composed of a main body 2201, acamera portion 2202, an image receiving portion 2203, operation switches2204, and a display portion 2205. The present invention can be appliedto the display portion 2205.

FIG. 6D shows a goggle type display that is comprised of a main body2301, display portions 2302, and arm portions 2303. The presentinvention can be applied to the display portion 2302.

FIG. 6E shows a player which uses a recording medium in which a programis stored (hereinafter referred to as a recording medium) and which iscomprised of a main body 2401, a display portion 2402, speaker portions2403, a recording medium 2404, and operation switches 2405. A DVD(Digital Versatile Disc), a compact disc (CD) or the like is used as therecording medium to enable the player to appreciate music and themovies, and play a video game or the Internet. The present invention canbe applied to the display portion 2402.

FIG. 6F shows a digital camera that is comprised of a main body 2501, adisplay portion 2502, an eye-piece portion 2503, operation switches2504, and an image receiving portion (not shown in the figure). Thepresent invention can be applied to the display portion 2502.

FIG. 7A shows a front type projector that is comprised of a projectionunit 2601, a screen 2602, and the like. The present invention can beapplied to a liquid crystal display device 2808 which is a partstructuring the projection unit 2601.

FIG. 7B shows a rear type projector that is comprised of a main body2701, a projection unit 2702, a mirror 2703, a screen 2704, and thelike. The present invention can be applied to the liquid crystal displaydevice 2808 which is a part structuring the projection unit 2702.

Illustrated in FIG. 7C is an example of the structure of the projectionunits 2601 and 2702 that are shown in FIGS. 7A and 7B, respectively.Each of the projection units 2601 and 2702 is comprised of a lightsource optical system 2801, mirrors 2802 and 2804 to 2806, dichroicmirrors 2803, a prism 2807, liquid crystal display devices 2808, phasedifference plates 2809, and a projection optical system 2810. Theprojection optical system 2810 is constructed of an optical systemincluding projection lenses. An example of a three plate system is shownin Embodiment 3, but there are no special limitations. For instance, anoptical system of single plate system is acceptable. Further, theoperator may suitably set optical systems such as optical lenses,polarizing film, film to regulate the phase difference, IR film, withinthe optical path shown by the arrows in FIG. 7C.

In addition, FIG. 7D shows an example of the structure of the lightsource optical system 2801 of FIG. 7C. In this embodiment, the lightsource optical system 2801 is composed of a reflector 2811, a lightsource 2812, lens arrays 2813 and 2814, a polarizing conversion element2815, and a condenser lens 2816. Note that the light source opticalsystem shown in FIG. 7D is an example, and it is not limited to theillustrated structure. For example, the operator may suitably setoptical systems such as optical lenses, polarizing film, film toregulate the phase difference, and IR film.

Thus, the application range for the present invention is extremely wide,and it may be applied to electronic equipment in all fields. Further,the electronic equipment of this Embodiment can be realized with acomposition that uses any combination of Embodiments 1 and 2.

Embodiment 4

An example of a single gate TFT was shown in Embodiment 1, but anexample of a double gate TFT will be shown here in Embodiment 4.Nonetheless, their structures are basically the same.

First, a conductive film is formed on a substrate 401 having aninsulating surface, and then patterning is carried out to thereby form ascanning line 402. (see FIG. 8A) The scanning line 402 also functions asa light shielding layer to protect an active layer, which will be formedlater, from light. A quartz substrate is used as the substrate 401, anda laminate structure of a poly-silicon film (having a film thickness of50 nm) and a tungsten silicide (W—Si) film (having a film thickness of100 nm) is used for the scanning line 402. In addition, the poly-siliconfilm protects the substrate from contamination from the tungstensilicide film.

Next, insulating films 403 a and 403 b are formed to a film thickness ofbetween 100 and 1000 nm (typically between 300 and 500 nm) covering thescanning line 402. (see FIG. 8B) Here, a 100 nm thick silicon oxide filmformed by employing the CVD method and a 280 nm thick silicon oxide filmformed by employing the LPCVD method are laminated.

An amorphous semiconductor film is then formed with a thickness of 10 to100 nm. A 69 nm thick amorphous silicon film is formed here by using theLPCVD method. Next, as a technique to crystallize the amorphoussemiconductor film, the crystallization technique disclosed in JapanesePatent Application Laid-open No. Hei 8-78329 is employed to performcrystallization of the amorphous semiconductor film. The techniquedisclosed in the above publication is a crystallization technique inwhich a metal element for promoting crystallization is selectively dopedinto the amorphous silicon film, and then heat treatment is carried out.By carrying out the heat treatment, a crystalline silicon film in whichits formation starts from the doped region is formed. Nickel is usedhere as the metal element for promoting crystallization. Heat treatmentfor crystallization (600° C., 12 hours) was performed after theperforming of a heat treatment for releasing hydrogen (450° C., 1 hour).

Thereafter, Ni is gettered from a region as the active layer of the TFT.The region as the active layer of the TFT is covered with a mask(silicon oxide film), and then phosphorus (P) is doped into a portion ofthe crystalline silicon film. Next, heat treatment is performed under anitrogen atmosphere at 600° C. for 12 hours.

After removing the mask, patterning is performed to remove theunnecessary portions of the crystalline silicon film, thereby forming asemiconductor layer 404. (see FIG. 8C(1)) Note that a top view of thepixel after the formation of the semiconductor layer 404 is shown inFIG. 8C(2). The sectional view cut along the broken line A-A′ in FIG.8C(2) corresponds to FIG. 8C(1).

A mask 405 is formed next, and then phosphorus is doped into a portionof the semiconductor layer (a region as the storage capacitor) 406 toform the storage capacitor. (see FIG. 9A).

Then the mask 405 is removed, and after forming an insulating film forcovering the semiconductor layer, a mask 407 is formed. The insulatingfilm on the region 406 as the storage capacitor is then removed. (SeeFIG. 9B).

Thereafter, the mask 407 is removed and thermal oxidation is conductedto form an insulating film 408 a (gate insulating film). Through thermaloxidation, the final film thickness of the gate insulating film became80 nm. Note that an insulating film 408 b is formed thinner than thoseof other regions on the region as the storage capacitor. (see FIG.9C(1)) A top view of the pixel at this stage is shown in FIG. 9C(2). InFIG. 9C(2), the sectional view cut along the broken line B-B′corresponds to FIG. 9C(1). Further, the region shown inside the dashedline in FIGS. 9C(1) and (2) are portions in which the thin insulatingfilm 408 b is formed.

A channel dope process for doping an impurity element that imparts ap-type or an n-type conductivity at a low concentration into a regionthat is to become a channel forming region of the TFT is performed onthe entire surface or selectively. The channel dope process is a processfor controlling the threshold voltage of the TFT. Note that diborane(B₂H₆) is not mass separated but boron is doped by a plasma excited iondope method. Of course, the ion implantation method may be employed toperform mass separation.

Next, a mask 409 is formed on the insulating film 408 a and theinsulating films 403 a and 403 b to thereby form a contact hole to reachthe scanning line 402. (see FIG. 10A) Then the mask is removed after theformation of the contact hole.

A conductive film is formed next, and then patterning is performed toform a gate electrode 410 and a capacitor wiring 411. (see FIG. 10B) Alaminated structure of a silicon film (having a film thickness of 150nm) and a tungsten silicide film (having a film thickness of 150 nm),which have been doped with phosphorus, is used here. It is to be notedthat the storage capacitor, with the insulating film 408 b as adielectric, is composed of the capacitor wiring 411 and the portion 406of the semiconductor layer.

Then phosphorus is doped at low concentration in a self-aligning mannerusing the gate electrode 410 and the capacitor wiring 411 as a mask.(see FIG. 10C(1)) A top view of the pixel at this stage is shown in FIG.10C(2). In FIG. 10C(2), the sectional view cut along the broken lineC-C′ corresponds to FIG. 10C(1). The phosphorus concentration of thisregion doped at low concentration is adjusted so that it becomes 1×10¹⁶to 5×10¹⁸ atoms/cm³, typically 3×10¹⁷ to 3×10¹⁸ atoms/cm³.

A mask 412 is formed next, and phosphorus is doped at a highconcentration, thereby forming a high concentration impurity region 413that is to become a source region or a drain region. (see FIG. 11A) Thephosphorus concentration of this high concentration impurity region isadjusted so that it becomes 1×10²⁰ to 1×10²¹ atoms/cm³, (typically2×10²⁰ to 5×10²⁰ atoms/cm³). Note that a region of the semiconductorlayer 404 which overlaps with the gate electrode 410 becomes a channelforming region 414 and a region of the semiconductor layer 404 which iscovered by the mask 412 becomes a low concentration impurity region 415functioning as an LDD region. Then the mask 412 is removed after dopingan impurity element.

Although not shown in the figure, in order to form a p-channel TFTutilized in a driver circuit that is formed on the same substrate as thepixel, a region that is to become an n-channel TFT is covered with amask and then doped with boron to form a source region or a drainregion.

A passivation film 416 is formed next to cover the gate electrode 410and the capacitor wiring 411 after removing the mask 412. A siliconoxide film formed to a thickness of 70 nm is used for the passivationfilm here. Next, heat treatment is performed to activate the impurityelement that imparts a p-type conductivity or an n-type conductivitydoped at respective concentrations into the semiconductor layer. Heattreatment is performed at 850° C. for 30 minutes.

Next, an interlayer insulating film 417 made of an organic resinmaterial is formed. An acrylic resin film formed to a thickness of 400nm is used here. Then an electrode 418 and a source wiring 419 areformed after forming a contact hole to reach the semiconductor layer. InEmbodiment 4, the electrode 418 and the source wiring 419 are used for alaminated film of a three-layered structure composed of a 100 nm Tifilm, a 300 nm aluminum film containing Ti, and a 150 nm Ti film whichare formed in succession by sputtering (FIG. 11B(1)). In FIG. 11B(2),the sectional view cut along the broken line D-D′ corresponds to FIG.11B(1).

Then after performing the hydrogenation process, an interlayerinsulating film 420 made of acrylic is formed (FIG. 12A(1)). A 100 nmconductive film having light shielding characteristics is formed on theinterlayer insulating film 420, to thereby form a light shielding layer421. Following this, an interlayer insulating film 422 is formed, andthen a contact hole is formed to reach the gate electrode 418. A 100 nmtransparent conductive film (here it is an indium tin oxide (ITO) film)is formed and patterned to form pixel electrodes 423 and 424. In FIG.12A(2), the sectional view cut along the broken line E-E′ corresponds toFIG. 12A(1).

Accordingly, in the pixel portion, a surface area of the display region(pixel size 26 μm×26 μm) (aperture ration of 76.5%) can be secured,while the pixel TFT, which is formed from the n-channel TFT, is formed,and a sufficient storage capacitor (51.5 fF) can be obtained.

Note that Embodiment 4 is an example, and therefore, needless to say,the present invention is not limited to the process of this Embodiment.For example, a film formed from an element selected from the groupconsisting of tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), chrome (Cr) and silicon (Si), or from an alloy film of acombination of these elements (typically Mo—W alloy and Mo—Ta alloy) canbe used as the respective conductive films. Furthermore, a silicon oxidefilm, a silicon nitride film, a silicon oxynitride film, and a film madeof an organic resin material (such as polyimide, acrylic, polyamide,polyimide amide, and BCB (benzocyclobutene)) can be used as therespective insulating films.

The characteristic of the TFT thus obtained showed a satisfactory value.The TFT characteristic (V-I characteristic) is shown in FIG. 13. AnS-value shows an excellent value of 105.8 (mV/dec) since, particularly,the structure of the present invention is a dual gate structure. Inaddition, by fabricating the structure of the present invention, athreshold value (Vth) that indicates a voltage value at the startingpoint in the V-I characteristic graph is 0.946 V in the case of Vd=0.1 Vand 0.886 V in the case of Vd=5 V. Thus, there is a difference of 0.06which is extremely small. It can be said that the smaller the differenceis, the more short-channel effect is suppressed. Further, a mobility(μ_(FF)) shows an excellent value of 220 (cm²/Vs).

Embodiment 5

Embodiment 5 is characterized in that a scanning line 502 a is formed ona different layer from a gate electrode, and furthermore, a capacitorelectrode 502 b is formed on the same layer as the scanning line 502 ain order to increase the aperture ratio as well as enlarge the storagecapacitor. An example of the pixel structure of the present invention isshown in FIG. 14 and FIGS. 15A and 15B.

Note that the schematic cross-sectional structural views cut along thebroken lines A-A′ and B-B′ in FIG. 14 correspond to FIGS. 15A and 15B,respectively.

In FIG. 14, a gate electrode 506 patterned into an island shape isconnected to a scanning line 502 a through a contact hole 500 c formedat an insulating film. Further, a semiconductor film 504 is connected toa signal line 509 through a contact hole 500 a. In addition, thesemiconductor film 504 is connected to an electrode 510 through acontact hole 500 b. A region of the semiconductor film that is connectedto the signal line 509 or to the electrode 510 is referred to as asource region or a drain region. Further, a channel forming region isformed between the source region and the drain region, and the gateelectrode 506 is present on the channel forming region through a gateinsulating film. Note that the source region, the drain region, and thechannel forming region are not shown in the figure for simplification.

In Embodiment 5, in the case of forming the scanning lines 502 a on thelower layer of the gate electrode 506 as shown in FIG. 14, the scanningline 502 a will be provided on the lower layer of the semiconductor film504, thus it is made possible to function as a light shielding film. Inaddition, the storage capacitor is formed with a lower electrode as thesemiconductor film, an insulating film covering the semiconductor filmas a dielectric, and a upper electrode as a capacitor wiring 507. It isto be noted that the storage capacitor may be enlarged by partiallythinning the insulating film which covers the semiconductor film.

Further, the storage capacitor of Embodiment 5 can also be formed withthe capacitor electrode 502 b connected to the capacitor wiring 507,with the insulating film 503 as a dielectric, as shown in FIGS. 15A and15B. Accordingly, the storage capacitor can be efficiently secured andcontrast of a liquid crystal display device utilizing this pixelstructure can be improved. It is noted that reference numeral 501denotes a substrate, 502 denotes a gate insulating film (secondinsulating film), 508 denotes a third insulating film, and 511 denotes asignal line.

According to the structure of Embodiment 5, the TFTs of each pixel canbe a dual gate structure in which a gate electrode is provided on theupper and lower parts of the channel forming region through aninsulating film, and the parasitic capacitance formed by the scanningline and another wiring can be restrained while improving thecharacteristics of the TFTs by setting the film thickness of the firstinsulating appropriately.

A method of manufacturing the pixel structure shown in Embodiment 5 isnearly the same as that of Embodiment 1 or 4, and therefore descriptionsthereof are omitted here.

It is to be noted that Embodiment 5 can be freely combined with any oneof structures described in Embodiments 1 to 4.

Embodiment 6

Embodiment 6 discloses to increase the aperture ratio as well as enlargethe storage capacitor in case of decreasing a pixel size. In particular,the present embodiment is characterized in that the storage capacitor isformed of the light shielding film and the pixel electrode.

FIG. 16 is a cross sectional view showing the liquid crystal displaydevice of the present embodiment. Reference numeral 601 denotes asubstrate (TFT substrate), 602 denotes a scanning line, 603 denotes afirst insulating film, 604 denotes a semiconductor film, 605 denotes agate insulating film (second insulating film), 606 b denotes a gateelectrode, 606 c denotes a gate wiring, 606 a denotes a capacitorwiring, 607 denotes a third insulating film, 608 denotes an electrodefor connecting the pixel electrode 612 and the TFT through a contacthole formed in the third insulating film.

Reference numeral 609 denotes a fourth insulating film covering the TFT,610 denotes a light shielding film preventing the TFT from distortion bylight, 611 denotes a fifth insulating film, 612 denotes a pixelelectrode connected to the electrode 608 through a contact hole, and 613denotes an alignment film for orienting liquid crystal layer 614.

In FIG. 16, an opposing electrode 616 and an alignment film 615 areprovided on the opposing substrate 617. A light shielding film or acolor filter may be further provided on the opposing substrate 617.

As shown in FIG. 16, the storage capacitor of the present embodiment isconstructed by first storage capacitor formed of the capacitor wiring606 a, semiconductor film 604, and the insulating film 605 as adielectric, and second storage capacitor formed of the light shieldingfilm 610, pixel electrode 612, and the insulating film 611 as adielectric. It is noted that the insulating film 611 may be an organicresin film, or a inorganic insulating film such as silicon oxynitrideand silicon oxide, etc. And the thickness of the insulating film may beappropriately decided by the operator.

For example, even if the pixel size is set to 14 μm×14 μm, enoughstorage capacitor (about 100 fF), and an aperture ratio of 48.8% can besecured by constructing the pixel electrode as shown in FIG. 17B.

FIG. 17A denotes a top view at the step of forming an electrode 608, andFIG. 17B is a top view at the step of forming the light shielding film610 and the pixel electrode 612. The same reference numerals are used atthe part corresponding to FIG. 16.

It is to be noted that Embodiment 6 can be freely combined with any oneof structures described in Embodiments 1 to 5.

According to the present invention, a region (the region thatcorresponds to the A region in FIG. 19) that was conventionally used asa wiring region within the scanning line and the scanning line/capacitorwiring segregation region can be used as the storage capacitor. Further,by structuring the plurality of pixels connected to the respectivescanning lines thereby being connected to the individually independentcapacitor wiring, signal writing-in can be performed continuously toeach pixel and the neighboring pixel, and even in the case of performingthe above signal writing-in, each pixel does not receive the influenceof the writing-in electric current of the neighboring pixel. Inaddition, the electric load of the respective capacitor wirings isdispersed in a timely manner, thereby reducing the effective load. Thus,the demand for the capacitor wiring resistance is alleviated.

Consequently, according to the liquid crystal display device employingthe present invention, a liquid crystal display element having both ahigh aperture ratio and respective pixels having therein storagecapacitors which hold sufficient display signal electric potential isobtained. Accordingly, satisfactory image display can be obtained whileattaining small scale and power-saving devices.

1. A display device comprising a pixel portion, the pixel portioncomprising: a first wiring formed on an insulating surface; a firstinsulating film formed on the first wiring; a semiconductor film formedon the first insulating film; a second insulating film formed on thesemiconductor film; a gate electrode formed on the second insulatingfilm, and electrically connected to the first wiring; a third insulatingfilm formed over the gate electrode; and a signal line formed over thethird insulating film, and electrically connected to the semiconductorfilm.
 2. A display device comprising a pixel portion, the pixel portioncomprising: a first wiring formed on an insulating surface; a firstinsulating film formed on the first wiring; a semiconductor film formedon the first insulating film; a second insulating film formed on thesemiconductor film; a gate electrode formed on the second insulatingfilm, and electrically connected to the first wiring; a capacitor wiringformed over the second insulating film; a third insulating film formedover the gate electrode; and a signal line formed over the thirdinsulating film, and electrically connected to the semiconductor film.3. A display device comprising a pixel portion, the pixel portioncomprising; a first wiring formed on an insulating surface; a firstinsulating film formed on the first wiring; a semiconductor film formedon the first insulating film; a second insulating film formed on thesemiconductor film; a gate electrode formed on the second insulatingfilm, and electrically connected to the first wiring; a third insulatingfilm formed over the gate electrode; a signal line formed over the thirdinsulating film, and electrically connected to the semiconductor film; afourth insulating film formed over the signal line; and a lightshielding film formed over the fourth insulating film.
 4. A displaydevice comprising a pixel portion, the pixel portion comprising: a firstwiring formed on an insulating surface; a first insulating film formedon the first wiring; a semiconductor film formed on the first insulatingfilm; a second insulating film formed on the semiconductor film; a gateelectrode formed on the second insulating film, and electricallyconnected to the first wiring; a third insulating film formed over thegate electrode; a signal line formed over the third insulating film, andelectrically connected to the semiconductor film; a fourth insulatingfilm formed over the signal line; and a pixel electrode formed over thefourth insulating film.
 5. A display device comprising a pixel portion,the pixel portion comprising: a first wiring formed on an insulatingsurface; a first insulating film formed on the first wiring; asemiconductor film formed on the first insulating film; a secondinsulating film formed on the semiconductor film; a gate electrodeformed on the second insulating film, and electrically connected to thefirst wiring; a capacitor wiring formed over the second insulating film;a third insulating film formed over the gate electrode; a signal lineformed over the third insulating film, and electrically connected to thesemiconductor film; a fourth insulating film formed over the signalline; and a pixel electrode formed over the fourth insulating film.
 6. Adisplay device comprising a pixel portion, the pixel portion comprising:a first wiring formed on an insulating surface; a first insulating filmformed on the first wiring; a semiconductor film formed on the firstinsulating film; a second insulating film formed on the semiconductorfilm; a gate electrode formed on the second insulating film, andelectrically connected to the first wiring; a third insulating filmformed over the gate electrode; a signal line formed over the thirdinsulating film, and electrically connected to the semiconductor film; afourth insulating film formed over the signal line; a light shieldingfilm formed over the fourth insulating film; a fifth insulating filmformed over the light shielding film; and a pixel electrode formed overthe fifth insulating film.
 7. A display device according to any one ofclaims 1 to 6, wherein the first wiring comprises a gate wiring.
 8. Adisplay device according to any one of claims 1 to 6, wherein the secondinsulating film comprises a gate insulating film.
 9. A display deviceaccording to claim 8, wherein the gate insulating film comprises athermal oxidation film.
 10. A display device according to any one ofclaims 1 to 6, wherein the third insulating film comprises at least oneselected from the group consisting of silicon oxide, silicon nitride,and silicon oxynitride.
 11. A display device according to any one ofclaims 3 to 6, wherein the fourth insulating film comprises at least oneselected from the group consisting of an organic insulating material,silicon oxide, silicon nitride, and silicon oxynitride.
 12. A displaydevice according to claim 6, wherein the fifth insulating film comprisesan organic insulating material.
 13. A display device according to anyone of claims 2 and 5, wherein the capacitor wiring is in contact withthe second insulating film.
 14. A display device according to any one ofclaims 1 to 6, wherein the display device is a liquid crystal displaydevice.
 15. A display device according to any one of claims 1 to 6,wherein the display device is incorporated in at least one selected fromthe group consisting of a personal computer, a video camera, a mobilecomputer, a goggle type display, a player using a recording medium, anda digital camera.
 16. A display device comprising a pixel portion, thepixel portion comprising; a scanning line formed over a substrate; asemiconductor film formed over the scanning line, wherein thesemiconductor film includes a source region, a drain region, a channelforming region, and a region to be a lower electrode for a storagecapacitor; a gate electrode formed over the channel forming region; anupper electrode for the storage capacitor formed over the lowerelectrode; and a signal line formed over the gate electrode and theupper electrode, wherein the lower electrode has a first portion inparallel with and overlapped with the signal line, and has a secondportion in parallel with and overlapping the scanning line, and whereinthe upper electrode has a third portion in parallel with and overlappedwith the signal line, and has a fourth portion in parallel with andoverlapping the scanning line.
 17. A display device comprising a pixelportion, the pixel portion comprising: a scanning line formed over asubstrate; a semiconductor film formed over the scanning line, whereinthe semiconductor film includes a source region, a drain region, achannel forming region, and a region to be a lower electrode for astorage capacitor, and wherein the source region, the drain region andthe channel forming region overlap the scanning line; a gate electrodeformed over the channel forming region; an upper electrode for thestorage capacitor formed over the lower electrode; and a signal lineformed over the gate electrode and the upper electrode, wherein thelower electrode has a first portion in parallel with and overlapped withthe signal line, and has a second portion in parallel with andoverlapping the scanning line, and wherein the upper electrode has athird portion in parallel with and overlapped with the signal line, andhas a fourth portion in parallel with and overlapping the scanning line.18. A display device comprising a pixel portion, the pixel portioncomprising: a scanning line formed over a substrate; a semiconductorfilm formed over the scanning line, wherein the semiconductor filmincludes a source region, a drain region, a channel forming region, anda region to be a lower electrode for a storage capacitor; a gateelectrode formed over the channel forming region; an upper electrode forthe storage capacitor formed over the lower electrode; a signal lineformed over the gate electrode and the upper electrode; and a lightshielding film formed over the signal line, wherein the light shieldingfilm overlaps the semiconductor film, wherein the lower electrode has afirst portion in parallel with and overlapped with the signal line, andhas a second portion in parallel with and overlapping the scanning line,and wherein the upper electrode has a third portion in parallel with andoverlapped with the signal line, and has a fourth portion in parallelwith and overlapping the scanning line.
 19. A display device accordingto any one of claims 16 to 18, wherein the gate electrode contains atleast one selected from the group consisting of poly-Si, W, WSi_(x), Al,Ta, Cr, and Mo.
 20. A display device according to any one of claims 16to 18, wherein the upper electrode for the storage capacitor contains atleast one selected from the group consisting of poly-Si, W, WSi_(x), Al,Ta, Cr, and Mo.
 21. A display device according to any one of claims 16to 18, wherein the scanning line contains at least one selected from thegroup consisting of poly-Si, W, WSi_(x), Al, Ta, Cr, and Mo.
 22. Adisplay device according to any one of claims 16 to 18, wherein thesignal line contains at least one selected from the group consisting ofAl, W, Ti, and TiN.
 23. A display device according to any one of claims16 to 18, wherein the display device is a liquid crystal display device.24. A display device according to any one of claims 16 to 18, whereinthe display device is incorporated in at least one selected from thegroup consisting of a personal computer, a video camera, a mobilecomputer, a goggle type display, a player using a recording medium, anda digital camera.